The world is running out of inexpensive fossil fuels. To maintain present standards of living, it is imperative to find suitable substitutes for these fossil fuels. The conversion of biomass to liquid fuels, especially transportation fuels, is an attractive path towards the partial replacement of fossil fuels. The production of biofuels entails the conversion of an oxygen-rich source (biomass) to an oxygen-deficient source (liquid fuels). The oxygen is removed as water or carbon dioxide. Depending on the specifics of the conversion process, the water removed (termed process water) is contaminated with various inorganic and organic compounds. The discharge of this process water is regulated by local, state and federal laws.
The treatment of process water prior to discharge may entail considerable capital and operational costs. It is desirable to minimize these costs and to apply minimal treatments to the process water. Ideally, the conversion process itself should produce little contamination of the process water. In cases where the production of process water is unavoidable, this water should be ideally treated within the confines of the process so that the process water exits out ready to be discharged or used in another process. The US Environmental Protection Agency recommended process for the reduction of benzene, dichlorobenzene, toluene, xylene and other aromatic hydrocarbons in water includes passing process water through granular carbon and subjecting the resulting effluent to packed tower aeration in a column via an external air supply. The air and the effluent flow countercurrently through a high surface area packed tower to produce clean water. The process is capable of reducing the concentration of various organic contaminants in water to parts-per-billion (ppb) levels, however, it requires a separate process dedicated solely to waste water processing.
Accordingly, there is a need for a process water treatment for a biomass pyrolysis process which recycles a biochar product stream and requires minimal investment capital and operating costs.